1. Field of the Invention
The present invention relates to a walking assistance device which assists leg motion during walking or the like of a user (person) and a controller which controls the operation of the walking assistance device.
2. Description of the Related Art
Hitherto, as this type of walking assistance device, Japanese Patent Application Laid-Open No. 2007-29633 (hereinafter referred to as “patent document 1”), for example, discloses one proposed by the present applicant. This walking assistance device has a load transmit portion on which a user sits astride, foot-worn portions to be attached to the feet of the user, and leg links which connect the foot-worn portions to the load transmit portion. In this case, each of the leg links is constructed of an upper link member extended from the load transmit portion through the intermediary of a first joint, a lower link member extended from the foot-worn portion through the intermediary of a second joint, and a third joint which bendably connects the upper link member and the lower link member. Further, the third joint is driven by a drive source (actuator) mounted on the upper link member. The third joint is driven to cause load for supporting a part of the weight of the user (an upward translational force) to act on the body trunk of the user through the intermediary of the load transmit portion. Thus, a burden on a leg or legs of the user is reduced.
According to the walking assistance device disclosed in the aforesaid patent document 1, when a power source of an electric motor or the like serving as an actuator, is turned off while the load transmit portion is still disposed under the crotch of a user at the time of, for example, removing the walking assistance device from the user, the load transmit portion rapidly freely falls by gravity acting on the walking assistance device unless the user or an attendant or the like manually supports the load transmit portion. Further, there has been a danger in that an impact from the free fall damages the joints or the like of leg links and the load transmit portion or the like bumps against another object and breaks the object.
Further, in the walking assistance device disclosed in patent document 1, it is considered desirable in effectively reducing a burden on a leg or legs of the user to increase load to be applied to the user from the load transmit portion particularly in a state wherein the user has his/her knee or knees bent relatively deeply.
However, in the conventional walking assistance device, increasing the load to be applied to the user from the load transmit portion requires a relatively large driving force of an actuator. This has inconveniently resulted in an increased size or an increased weight of the actuator, making it difficult to achieve a smaller size and a reduced weight of the walking assistance device. In addition, there has been another inconvenience in that the actuator requires a relatively large driving force, leading to increased energy consumption by the actuator.